1. Field of the Invention
The present invention relates to a procedure to agglutinate copper concentrates in a gravel heap, to be later leached on a non-flooded bed, to which an agglutinating solution containing calcium chloride, and a second solution containing sulfate ion, are added.
2. Description of the Prior Art
The copper concentrate, usually obtained by flotation, can be currently processed in order to obtain metal copper, by using both pyrometallurgical and hydrometallurgical techniques. As indicated by its name, the pyrometallurgical techniques, by far the most common ones at present, correspond to processes using high temperatures such as roasting, smelting, conversion, and fire refining, to obtain metal copper. On the other hand, the hydrometallurgical techniques correspond to those processes using aqueous solutions for copper extraction. During the last decade, the interest in using hydrometallurgical processes to treat copper concentrates has significantly increased, as the environmentalist pressure has increased on the pyrometallurgical processes, which have a serious impact on the environment.
A number of processes, most of them patented, have been studied for hydrometallurgical treatment of the copper concentrates, to avoid them to be processed by the usual pyrometallurgical techniques. From the industrial point of view and to this presentation's interest, all the processes for hydrometallurgical treatment of the copper concentrates, can be divided into two major fields: reactor leaching and heap leaching, being the first one where a high number of new proposed processes exist. In spite of the high number of processes developed in reactors, none of them has become an alternative to the pyrometallurgical process to treat the copper concentrates.
On the other side, unlike the treatment of copper concentrates in reactors, heap leaching has shown to be a very valuable technique to treat a great amount of copper ores. Copper ore leaching, both for oxidized ores and some sulphide ores, is currently one of the essential pillars sustaining this metal production worldwide.
The procedure as referred to by this invention, corresponds to the use of the heap leaching method, as applied to concentrate leaching rather than or in addition to, copper ores. At this point, it should be stressed that copper concentrates are mainly composed of sulphide copper species, with a much smaller component of oxidized species.
Next, a brief summary of the procedures as described in papers and patents for reactor copper concentrate leaching will be presented, as well as the attempts made to treat these concentrates in heaps, making use of its higher advantages, both practical and economical.
First, for reactor copper concentrate leaching, a series of chemical and biochemical reactions have been proposed, which are either oxidizing or oxidation reaction catalysis, able to dissolve the sulphide species containing copper. Among these are, mainly: oxidation by means of a ferric ion, or through the chlorine—copper ion, nitric oxides, gas chlorine, gas oxygen, and ferrooxidans bacteria.
Apart from the bacterial leaching processes, which are those closest to an industrial application, the following processes are currently under development, even though none of them shows the progress required for a high tonnage industrial application: pressure leaching, hot leaching, nitro-catalyst leaching, and bromide-chloride leaching. All these processes require the concentrate to be finely divided.
Of all of them, those of interest to this discussion are the processes using the ferric ion, and the copper ion, in a chloride environment, because use of the chloride ion is the basis of the present invention.
The use of chloride to help dissolve the copper concentrates has been studied, and patents have been generated for over 100 years. Leaching sulfides by using chlorides such as FeCl3 and CuCl2, is currently recognized as one of the most effective methods to produce concentrated solutions, from which copper is directly extracted, with the additional advantage of obtaining sulfur as an elementary substance.
Among the known and patented processes using reactors to leach the concentrates, are the following:
The Canmet process, Minemet Recherche and Broken Hill process use sulfate-chloride solutions. The solutions obtained are treated by solvent extraction in the traditional manner.
The Cymet process uses a FeCl3 and CuCl2 mixture as leaching media. The CuCl obtained is precipitated from the solution and reduced to metallic Cu by using a hydrogen flow in a fluidized bed reactor.
In Duval Corporation's Clear process, copper chloride is used as leaching means, along with brine containing potassium and sodium. Iron is precipitated in a second pressurized stage as potassium jarosite. Copper is electrolyzed in cuprous state to obtain copper crystals into the cathode. Copper chloride is regenerated from the cuprous in the anode, and returned to leaching.
The USBM process is similar except for the use of ferric chloride rather than copper chloride, and copper is dissolved as cuprous chloride. Copper is directly produced by electrolysis, in a diaphragm cell. Reagent is regenerated in the cell anodic compartment.
The Dextec process produces the anodic copper to dissolve in the presence of oxidizers. This reaction takes place in a diaphragm cell. The Cu sponge obtained as deposit in the cathode compartment contains all the impurities of the starting material.
The Elkem process is used to leach complex Cu, Zn and Pb concentrates in a countercurrent ferric and copper chloride solution. Cu is recovered, as a sponge, by EW. In a variation of this process, a CuCl2 is produced, from which copper is separated by SX before the EW stage, in which the quality of the copper produced is improved. In this process, the Zinc is extracted from the leaching solution by using tributilphosphate. The Pb is precipitated as PbCl2. The process is quite complicated, as problems exist related to the SX circuit and the shape of the metal obtained is not suitable for direct sales without an additional treatment.
The Cuprex process uses a NaCl and FeCl3, based solution to dissolve the copper sulfides, obtaining a CuCl2 solution. The Cu is extracted by using SX in chloride media, in three countercurrent stages. Re-extraction is carried out by using pure water and producing a concentrated CuCl2 solution, which is transferred to a diaphragm cell. The Cu produced is granular copper (the commercial cathode) and the operation is rather complex.
The Intec process carries out leaching by using an oxidizing chloride solution containing bromide chloride (Halex). Once the solution has been purified by using lime, granular Cu is extracted by electrolysis in an ion-selective membrane cell. The Cu as produced, even though of good chemical quality, cannot be commercialized without an additional treatment.
All these processes use vessels or reactors, generally agitated, and at a relatively high temperature, to obtain the oxidizing and dissolving reactions of the copper sulfides. The reactors agitated have several disadvantages, which generally make the process to be non-feasible. First, most of the sulfides are resistant to leaching, or difficult to leach, so they require very long reaction times and, consequently, equipment is very big and expensive. Second, a high power supply is required to maintain the solids suspended and mixed. Also, leaching in agitated tanks is carried out in aggressive environments by using concentrated reagents, and often at very high temperatures. This makes the reactor to be very sophisticated and expensive.
On the other hand, and compared to the reactor treatment, there exists the heap leaching treatment to process sulphide ores. This procedure is clearly simpler and cheaper than that of the reactors, since it does not require sophisticated equipment, or high temperatures, or pressures higher than the atmospheric one. The time frames involved, however, are longer than those involved in reactors. In spite of this, the investment required is much smaller, since in this case the reactor is the heap itself, the forming of which is much cheaper than that of a reactor.
Disregarding the fact that heap leaching is widely used in the industry, both for treating oxidized ores and some sulphide ores, the stockpile concentrate leaching is just in its experimental stage.
This, because a pile of pure concentrate, in itself, can not form a stable heap without a previous treatment. When you try to do this, a number of problems related to the flow of the irrigating solution arises, such as canalization, water stagnation, and poor drainage, all this due to the small size of the particles of which it is composed. For this reason, alternate ways to maintain a concentrate heap that is structurally stable have been studied.
Various attempts to agglomerate the concentrate particles to each other through the well known pelletizing process, by using water with or without an agglomerating agent, are known. Initially, these pellets can be effectively located to form a stockpile. However, since most of the mineral compounds forming the pellet react to leaching, these quickly loss their consistence and, eventually, the stockpile collapses.
An alternate procedure partially solving, or at least diminishing the disadvantages already mentioned, consists of having the concentrate particles adhered to a base material. This latter can be an artificial material, or a stony material, such as ore, discarded ore or rock, barren material, gravel, etc., crushed to the appropriate size.
Some processes using this concept have been recently developed. For example, U.S. Pat. No. 6,063,158 by Sharp et al. year 2000, uses a polyethylene sphere packing called “Bioballs”, which have the advantage of having a large external surface to which the concentrate particles can adhere. In this patent, the concentrate is mixed with graphite and a bacterial nutrient before adhering to the sphere packing, then the set is loaded on a heap and subjected to bacterial leaching, the same as if it was a mineral stockpile. In this case, a polyethylene-metacrilate polymer is used as a binding agent.
On the other hand, U.S. Pat. No. 6,083,730 by Kohr, year 2000, uses a similar concept to treat sulfide concentrates, but instead of using an artificial substratum as that in the paragraph above, it uses a set of coarse particles, which may correspond to washing, gravel, or other rock. Once the concentrate particles have adhered to the particles forming the coarse substratum, a stockpile is built and the concentrate bioleaching takes place. Here, the author mentions the possibility of adding an adherent polymer, even though he ensures that this is not necessary when the concentrate is wet, as a slurry. This same author has a number of patents in the USA, covering this subject, however, they refer to gold ore or copper concentrate bacterial leaching, and in no case to chemical leaching.
The idea of using an artificial or natural packing to obtain various hydrometallurgical reactions is not new. It began as a way to provide a base for bacterial growth through the formation of a biofilm, which has been proven even at an industrial level.
Unlike all the above, the invention described below refers to a new process to adhere the concentrates to the coarse particles, followed by a non-bacterial process based only in chemical reactions, the purpose of which is treating any copper concentrates by hydrometallurgical processing, as described below.